Electric motors commonly include a stationary component called a stator and a rotating component called a rotor. The rotor rotates within (or around) the stator when the motor is energized with a driving waveform. When the driving waveform is removed from the motor, the rotor may coast to a standstill over time due to the inertia of the rotor and anything coupled to the rotor.
In many motor applications, it is desirable to determine when a motor's rotor has stopped rotating so the rotor can be driven in the opposite direction, at a different speed, etc. For example, in washing machine applications, it is desirable to know when the washing drum motor has stopped rotating after a high speed spin cycle so that the washing machine may be unloaded or switched to a slower speed wash or rinse cycle.
Motor shaft sensors such as Hall effect sensors are often used to detect motor stoppage. However, such sensors increase the cost and complexity of motors and are therefore not desirable for many lower cost applications such as washing machine motors.
Sensorless techniques have also been developed for detecting motor stoppage. Such techniques typically employ various algorithms for estimating when a rotor stops based on measured electrical parameters. Unfortunately, such techniques are less accurate or don't work at all when a motor is being initially powered-up or braked or when the motor experiences a fault condition.
Simple time delay circuits are also often used to ensure motor stoppage. Such circuits require that a selected time period lapse after a driving waveform is removed from the motor before the rotor is assumed to be stopped. This unfortunately wastes time because the time delay is often longer than necessary to account for the maximum possible coast time of the motor.
The above section provides background information related to the present disclosure which is not necessarily prior art.